1. Field
The present disclosure relates generally to microprocessor-based drivers for light emitting diode (LED) bulbs, and more specifically to microprocessor-based drivers for LED bulbs that enable the LED bulb to emit light at different levels of brightness.
2. Description of Related Art
Conventional incandescent light bulbs that have three lighting levels (“three-way light bulbs”) include two filaments; in the minimum illumination setting a low wattage filament is energized, in the medium illumination setting a medium wattage filament is energized, in the high illumination setting both filaments are energized. The illumination setting is selected by energizing a first input connected to the low wattage filament, energizing a second input connected to the medium filament, or energizing both the first and second inputs.
The conventional incandescent three-way light bulb has three electrical contacts, hot1, hot2, and neutral. A switch, contained in the lamp base, connects terminal hot1 to mains power (e.g., a 120 VAC 60 Hz signal in the United States) in the low power case, connects hot2 to mains power in the medium power case, and connects both hot1 and hot2 to mains power in the high power case. Terminal hot1 is connected to the low wattage filament and terminal hot2 is connected to the medium wattage filament. Thus, either or both filaments may be selected to provide three levels of illumination.
One method for reproducing the same functionality of the incandescent three-way light bulb in an LED bulb is to have two sets of LEDs with each set having its own driver connected to a different hot input. However, this requires having two driver circuits, which increases costs and increases space requirements that are limited when implementing LED bulbs in typical form factors of standard light bulbs. Therefore, it is desirable to connect multiple hot inputs to a single driver circuit. However, this requires the driver circuit to sense which of two terminals are energized and set the supply current of the LEDs accordingly. This could be done by inserting a component in series with each input and sensing the voltage drop across this series component. While this technique may work in principle, it would introduce power losses in the series component. Additionally, this technique requires many additional parts to amplify and detect the voltage. These parts increase the cost of the LED bulb, and are therefore undesirable.